DESCRIPTION (adapted from the application): Lung surfactant is a surface active material that stabilizes the alveoli. It is synthesized and secreted by lung epithelial type II cells. Earlier signal transduction events prior to activation of protein kinases are well established in lung surfactant secretion. However, two essential steps involved in the later stages of secretory processes, including the transport of lamellar bodies to and fusion with the plasma membrane, have not been widely described. The long-term objective of this proposed project is to elucidate the molecular mechanisms of lung surfactant secretion from type II cells. Previous studies indicate that annexin II, an F-actin and phospholipid-binding protein, is a critical component in membrane fusion during surfactant secretion. In a continuation of exploring mechanisms of annexin II-mediated fusion of lamellar bodies with plasma membrane, SNARE proteins are now included as part of the molecular machinery for exocytosis of lamellar bodies. Specific Aim 1 of the present application is to establish functional roles of SNARE proteins in lung surfactant secretion using various techniques including reconstitution from permeabilized type II cells, neutrotoxin effects, antibody neutralization, peptide inhibition and antisense oligonucleotides. Specific Aim 2 will be achieved by determining physical and functional interactions of annexin II with SNARE proteins in type II cells. Specific Aim 3 is to investigate another role of annexin II in surfactant secretion, i.e. facilitating reorganization of cytoskeleton and thus the transport of lamellar bodies from the base of the cells to the apex. Finally, Specific Aim 4 is to examine two novel post-translational modifications of annexin II, S-nitrosylation and nitration, and their effects on lung surfactant secretion. Deficiency of lung surfactant is the cause of respiratory distress syndrome in premature infants. Accomplishing the goals of this proposal will advance the understanding of molecular mechanisms of lung surfactant secretion and may give a valuable insight to the therapy of pulmonary diseases such as neonatal respiratory distress syndrome.